1. Field of the Invention
The present invention relates to a process for treating shredder dust and separating and recovering valuable materials for recycling. It further relates to a process for crushing shredder dust, separating and recovering valuable metal and non-metal materials, and submitting them to resource recycling.
2. Description of the Related Art
The term "shredder dust" is a general name for the non-metallic refuse residues from crushed material from automobiles, home appliances, and the like produced by a crusher mainly comprising a hammer mill, followed by removing removable metals from the crushed product. When automobiles, home appliances, and the like are fed into a hammer mill, rotating circular rotors with hammers crushes the automobiles, home appliances, and the like, and discharge disintegrated metal and non-metal pieces from a grid beneath the crusher. The size of the crushed material differs depending upon the opening sizes of the grid beneath the crusher but is commonly about 75.times.110 mm to 100.times.200 mm, in general, oblong-shaped.
The crushed material can be generally classified into 4 types: 1) light waste, the components collected and accumulated by a dust collector; 2) a ferrous component separated and accumulated by a magnetic drum or the like; 3) a non-ferrous waste, that is non-ferrous metals, such as aluminum, copper, lead etc., separated, recovered, and accumulated by an automatic non-ferrous separator, such as STEINERT separators NE 50/NE 150, which function according to the eddy-current principle; and 4) heavy waste, that is a separated and accumulated stainless steel and heavy dust components which are inseparable by an automatic non-ferrous separator. Among these, the combination of 1) light waste and 4) heavy waste is shredder dust.
The shredder dust heretofore has been disposed of by such methods as 1) hauling it as collected to a controlled disposal facility for discarding; 2) shaping and compacting it into a cylindrical form by a twin-screw compactor and transporting it to a disposal facility for discarding; 3) storing it on the company site; 4) compressing it by a press machine and packaging the shredder dust using vinyl tape to be stored on the company site; or 5) subjecting it to the recovery of the metals by an incinerator equipped with a dry still furnace, thereby combusting the shredder dust and using the heat of combustion generated for power generation and so on. From among these methods, the combustion-power generation disposal process 5) is not presently used much and the shredder dust is commonly discarded at disposal facilities.
However, the shredder dust, which is disposed of in this manner, still contains about 10-15% by weight of stainless steel or like metal and about 10-15% by weight of inorganic oxides such as silica, alumina, and the like; and these valuable materials are currently disposed of as waste. It is a challenge for the future in terms of waste disposal and resource recycling to further recover the valuable materials from shredder dust and to reduce the load on the final disposal facility. In terms of waste treatment and resource recycling, automobiles and home appliances among type 1 designated products of the Disposal and Recycle Law of Japan are positioned to be the main pillars of a recycle system construction. In this aspect as well, retreatment of shredder dust and reuse of resources is an important subject.